Where does fat go when you burn it?

Do you sweat it out, pee it out or what?

None of the above: The cells merely shrink, their contents ‘burned’ for fuel, and any waste from this process cleared out of your bloodstream through the usual manners: sweat, urine, etc. To the best of my knowledge, tissues once expanded or forced to grow new cells (think of the skin on a person who has lost a large amount of weight, or a woman’s abdomen after giving birth to twins or triplets) never return to their original size because the new cells are there forever.

Im finding that hard to believe given how thin the skin seems to get with some of the ‘biggest loser’ types and the like?

As in while it might retain some thickness, a fair bit of shrinkage seems to be possible?


Fat consists of long lipid chains of Carbon and Hydrogen. When burned with Oxygen, it produces CO2, H2O and energy. Both the CO2 and the H2O are exhaled.

The H20 isn’t necessarily exhaled… it can be re-used by the body, or disposed of in the other usual ways (urination, sweat). Water produced as the end result of this sort of process is called metabolic water, though it’s no different from any other water.

Slight tangent: Camels don’t actually store bags of water in their humps. Instead, they have large masses of fatty tissue, and can live from their metabolic water alone for moderate periods of time.

A woman I used to work with explained to me that the amount of fat in the world is unchanging. She insisted that her refusal to diet saved some other woman from gaining whatever weight she lost. What a hero.

Correct. By weight, carbon makes up the greatest percentage of the fat. This is converted to CO2 and leaves the body via the lungs.

lazybratsche is correct as to the fate of metabolic water.